The present invention relates to an improved supercritical fluid extraction process. Specifically, the process provides improved methods for extraction of solutes from powdered egg substrates wherein the high costs of supercritical fluid extraction are reduced by increasing the flow rate of the supercritical fluid through the substrate, without sacrifice of solute mass transfer.
Supercritical fluid extraction is a very attractive process for removing either valuable or unwanted components from a wide variety of substrates. Supercritical fluid extraction is desirable because it leaves no solvent residues in either the substrate or the extract, does not create "still-bottoms" or stack emissions and is friendly to the environment.
Supercritical fluid extraction is rarely practiced on a large commercial scale with the decaffeination of coffees and teas, the extraction of hops essence and some other flavor extractions as notable exceptions. The major obstacle to large scale supercritical fluid extraction processes is the relatively high cost of those processes which is due in pan to low solubility of many target solutes in common supercritical fluids, prohibitive capital expenses and the protracted time which is required for the extraction to be accomplished.
The extraction time is dependent on the solubility of the solute, transfer of the solvent into the particle of substrate, transfer of the solute-laden solvent out of the substrate particle, and the flow rate at which the supercritical fluid can be pumped through the bed of substrate. Powdered materials in particular are subject to variable extraction rates in supercritical fluid extraction processes because powdered substrates tend to suffer from channelling and compaction of the substrate particles such as against the discharge plate of the supercritical fluid extraction pressure vessel.
Of interest to the present application is the process by which egg solids including egg yolk are processed by spray drying to produce a dried powder which can be further processed or can be reconstituted in the production of food products. Spray dried egg particles are characterized by mean particle sizes of about 0.1 millimeters, a relatively low degree of porosity and a relatively high bulk density. Such spray dried particles tend to suffer from compaction and channelling and provide resistance to fluid flow during supercritical fluid extraction.
Accordingly, there exists a desire in the art for a means of increasing the flow rate of supercritical fluid through a bed of substrate in such a way as to minimize reductions of solute mass transfer.